It is a common manufacturing practice to apply coatings of paint or other decorative or protective coatings to large subassemblies prior to final assembly of the completed product. For example, in the manufacture of automobiles, the body of the automobile will be formed and assembled, and then painted. Other automotive subassemblies such as suspension parts, undercarriages, or closures for the automobile (such as the doors, hood, and trunk lid) are separately manufactured and painted, and are assembled with the painted automobile body to form a complete automobile.
In most cases, the subassemblies of the automobile will be secured to the auto body by threaded fasteners. However, the use of threaded fasteners often presents difficulties in final assembly. For example, in the case of assembling a door into a body, one of the matching threaded fasteners, for example, a female fastener, may be located inside a door pillar. The door pillar in a modern automobile of unibody construction very often is a hollow metal part which may be completely enclosed after manufacture of the vehicle body. In order to provide a female fastener inside the pillar it is necessary to mount the female fastener, for example, by welding, inside the pillar when the body is being manufactured.
Due to variations in manufacturing tolerances, a degree of position adjustment for the female fastener must be provided so that the door and body may be properly aligned during final assembly. Position adjustment is provided by using a female fastener which is a cage nut, which is usually a nut encaged in a structure that is attached to the inside of the door pillar. The nut is provided with a range of movement within the encaging structure so that when the door is assembled to the body, the alignment of the door and the body can be adjusted until they meet manufacturing standards.
Cage nuts are also frequently used in situations where the nut is not completely enclosed. In these situations the use of a cage nut welded onto the body prior to final assembly reduces the time needed for final assembly of the automobile.
It has been found however, that during the step of painting and baking paint on the body of the auto, that the nut will often weld or adhere to the cage. This paint welding creates problems in the step of assembling and aligning the door or other subassembly with the body, because the nut no longer has any freedom of movement. It can be difficult to free the paint welded nut from the cage if it is in an enclosed space. Consequently, the final assembly of the automobile will be slowed while these parts are freed up enough so that the door or other subassembly can be properly aligned and assembled with the body.
One solution to this problem has been proposed, and that is the application of a coating of polytetraflouroethylene (PTFE) to the parts needing protection from paint welding, usually to the base of the nut. However, this procedure has been found to be costly because of the expense of the PTFE material. In addition, the presence of PTFE is undesireable on the joining surfaces of a nut or washer, as it reduces the frictional locking effect of the nut against the clamped surface.